Transit Time Estimation Research Articles

Small intestinal development in the young chick: Crypt formation and enterocyte proliferation and migration

1. Post-natch mucosal development was examined in the chick small intestinal epithelium using immunostaining with proliferating cell nuclear antigen (PCNA) and 5-bromo-2-deoxyuridine (BrdU). 2. On the day of hatching jejunal crypts were small and a single crypt per villus was observed. However, during the 108 h post-hatch crypts developed rapidly, branching and increasing in size, cell numbers and cell size. 3. Almost all epithelial cells in the small intestine of the hatching chick were proliferating, as indicated by PCNA and BrdU, while more than 80% of proliferating cells were localised in the crypts after 108 h post hatch. 4. Estimate of villus cell transit time using BrdU was only possible from 48 h post-hatch when villus transit time was 72 h in the jejunum, whereas at 336 h transit time was 96 h. 5. In the 108 h post hatch a rapid transition occurs from total jejunal epithelial cell proliferation and immature crypts to a defined proliferative zone in the crypts, with constant division and migration.

Quasi‐Lagrangian investigation into dimethyl sulfide oxidation in maritime air using a combination of measurements and model

Using a combination of field measurement data and a modified photochemical box model, strong evidence is presented to suggest that the rate of daytime oxidation of dimethyl sulfide (DMS) by OH radicals is insufficient to describe the measured conversion. Quasi‐Lagrangian measurements were made at two sites in the eastern Atlantic (Research Vessel and Mace Head Research Station, Ireland) as part of the Atmospheric Chemistry Studies in the Oceanic Environment (ACSOE) program. Periods of connected flow between the two sites were identified, air parcel transit times were estimated, and measurements of the main DMS oxidation products (MSA, SO2, and nss‐SO42−) were compared with model predictions to establish whether the model's chemical mechanism could account for observed changes. The main finding was that during daytime periods with maritime air masses, the model failed to predict a sufficient increase in DMS oxidation products during the estimated transit time. This was despite a tendency to overprediction of the progress of nitrogen chemistry during air mass advection, and independent checks on the model estimates of hydroxyl radical concentrations through measurements. In the light of this, the involvement of halogen species (most probably halogen oxides) or heterogeneous oxidation processes is tentatively suggested as the cause of enhanced daytime DMS oxidation in the marine boundary layer (MBL). Increasing the rate constant for the OH + DMS reaction by a factor of 3.3 (as a crude way of simulating parallel channels of DMS oxidation) permitted model results to reproduce the measurements very much more closely.

Iodine-129 Time Series in Danish, Norwegian and Northwest Greenland Coast and the Baltic Sea by Seaweed

The concentrations of129I and127I were determined in archived time series seaweed samples from Klint in the Kattegat, Bornholm in the Baltic Sea, Roskilde Fjord in Zealand of Denmark, Utsira in the western Norwegian coast and NW Greenland by neutron activation analysis. The results indicate that the129I levels in all locations investigated are one to three orders of magnitude higher than the fall-out background and strongly dominated by the discharges from reprocessing facilities at La Hague and Sellafield. The129I/99Tc ratio is applied to estimate the origin of and transit times of129I. Transit times of129I are estimated to be 1–2 years from La Hague to Klint and Utsira and 9–14 years to NW Greenland. Transfer factors of129I are calculated to be 54yrm−3from La Hague to Klint, 60yrm−3to Utsira and 1·2yrm−3to NW Greenland. Based on the estimated transit times, transfer factors and annual discharge data of radionulides from the reprocessing facilities, the variations of129I concentrations and129I/99Tc and129I/137Cs ratios are modelled. Except129I/137Cs, others are in a good agreement between the modelled and measured values.

Error analysis of classic colonic transit time estimates.

Estimates of colonic transit times (CTT) through the three colonic segments, right colon, left colon, and rectosigmoid, are commonly based on radiopaque markers. For a given segment, CTT is usually calculated from just the number of markers visible in that segment on abdominal X-rays. This procedure is only strictly valid for the theoretical, but unrealistic, case of continuous marker ingestion (i. e., not for a single or once-daily ingestion). CTT was analyzed using the usual estimate of the mean CTT of one marker and also using a new, more realistic estimate based on the kinetic coefficients of a three-compartment colonic model. We directly compared our compartmental approach to classic CTT estimates by double-marker studies in six patients. We also retrospectively studied CTT in 148 healthy control subjects (83 males, 65 females) and 1,309 subjects with functional bowel disorders (irritable bowel syndrome or constipation). Compared with the compartmental estimates, the classic approach systematically underestimates CTT in both populations, i.e., in patients and in healthy control subjects. The relative error could easily reach 100% independent of the site of colonic transit delay. The normal values of total CTT are then 44.3+/-29.3 instead of 30.1+/-23.6 h for males and 68.2+/-54.4 instead of 47.1+/-28.2 h for females.

Relation of Pathways and Transit Times of Recharge Water to Nitrate Concentrations Using Stable Isotopes.

AbstractOxygen and hydrogen stable isotope values of precipitation, irrigation water, soil water, and ground water were used with soil‐moisture contents and water levels to estimate transit times and pathways of recharge water in the unsaturated zone of a sand and gravel aquifer. Nitrate‐nitrogen (nitrate) concentrations in ground water were also measured to assess their relation to seasonal recharge. Stable isotope values indicated that recharge water usually had a transit time through the unsaturated zone of several weeks to months. However, wetting fronts usually moved through the unsaturated zone in hours to weeks. The much slower transit of isotopic signals than that of wetting fronts indicates that recharge was predominantly composed of older soil water that was displaced downward by more recent infiltrating water. Comparison of observed and simulated isotopic values from pure‐piston flow and mixing‐cell water and isotope mass balance models indicates that soil water isotopic values were usually highly mixed. Thus, movement of recharge water did not occur following a pure piston‐flow displacement model but rather follows a hydrid model involving displacement of mixed older soil water with new infiltration water. An exception to this model occurred in a topographic depression, where movement of water along prelerential flowpaths to the water table occurred within hours to days following spring thaw as result of depression‐focused infiltration of snow melt. In an adjacent upland area, recharge of snow melt occurred one to two months later. Increases in nitrate concentrations at the water table during April‐May 1993 and 1994 in a topographic low‐land within a cora field were related to recharge of water that had infiltrated the previous summer and was displaced from the unsaturated zone by spring infiltration. Increases in nitrate concentrations also occurred during July‐August 1994 in response to recharge of water that infiltrated during May‐August 1994. These results indicate that the largest ground water nitrate concentrations were associated with recharge of water that infiltrated into the soil during May‐August, when most nitrogen fertilizer was applied.

Plutonium Activity Ratios in Plankton: New Evidence of Hold-Up Time in Irish Sea Sediments

The determination of activity ratios for radioisotopes of different half-lives can be used to estimate transit times from a point source to locations further away. For conservative elements, this time is approximately equivalent to the net hydrological transport. However, for non-conservative elements such as plutonium, the additional influence of biogeochemical processes decreases the net transport time. In this study, 241Pu and 239,240Pu concentrations in Irish Sea plankton samples, collected in May 1994, were determined and the 241Pu/239,240Pu ratios calculated. Plutonium-239,240 was measured using a standard method by ion exchange chromatography and alpha counting, and 241Pu was determined by liquid scintillation counting using the disk-supported technique. The latter showed some methodological problems, which are briefly discussed. The 241Pu/239,240Pu ratios gave an estimate of the "transit time" from Sellafield to the different sampling points. In fact, this time represents the age of plutonium in plankton, i.e., the time lag between release from Sellafield and detection at the different sampling stations. The mean plutonium age was 17±2 years (n = 10) and 18.6±0.8 years (n = 13) in phytoplankton and zooplankton, respectively. The spatial distribution was reasonably homogeneous over the Irish Sea. The assimilation-elimination processes of plutonium in plankton are rather rapid. Therefore, it may be assumed that, in this time scale, the plutonium concentrations were in equilibrium with surrounding waters. Thus, it is concluded that plutonium was rather old because resuspension-sedimentation processes had occurred that delayed its transport within the Irish Sea. Therefore, the age of plutonium in plankton represented the hold-up time of plutonium in the sediments from the Irish Sea.

Using nonlinear regression to estimate parameters of dark adaptation.

An objective technique for estimating the kinetics of dark adaptation is presented, with which one can evaluate models with multiple parameters, evaluate several models of dark adaptation simultaneously, and rapidly analyze large data sets. Another advantage is the ability to simultaneously estimate transition times and rates of sensitivity recovery. Finally, this nonlinear regression technique does not require that the distributional properties of the data be transformed, and thus, parameter estimates are in meaningful units and reflect the actual rate of recovery of sensitivity.

Magnetic Resonance Angiography

Magnetic Resonance Angiography

Handling-induced delay and downstream movement of adult chinook salmon in rivers

We provide evidence that adult chinook salmon Oncorhynchus tshawytscha handled in riverine studies migrate differently upon release from their uncaptured peers. Adults with radio transmitters were released into the Kenai River, Alaska in July 1996 and 1997 while migrating chinook salmon were counted with split-beam sonar. Of known upstream migrants, 72% in 1996 and 46% in 1997 dropped downstream at least 3 km and typically delayed their upstream migration by 4–5 d with some delaying beyond 30 d. In contrast, at most 9% of migrants counted with the sonar were moving downstream. Delay, mortality rates, rates of transmitter failure, and capture rates in downstream fisheries were similar to statistics from other studies. No evidence was found to link downstream movement and delay to size, sex, or migratory timing of chinook salmon. Handling-induced behavior will bias estimated transit times and can bias abundance estimates from capture–recapture experiments, but should not bias estimates of migratory timing or distribution of spawning chinook salmon within a watershed.

On-Line Estimation of Transit Time Using Artificial Neural Networks

The use of artificial neural networks (ANNs) for transit time estimation is investigated. ANNs are proposed as an alternative to widely employed traditional techniques such as cross correlation and the cross spectrum, which are sensitive to the presence of noise and require a large volume of data for their calculation. The ANN employed is based on interactive activation and competition and has been found able to correctly estimate the current transit time from short records of signals generated by simulation, quickly follow changes in transit time, and detect when the transit time falls outside a predefined expected range. By appending a backpropagation ANN, the on-line estimation of decimated transit times is also allowed.

Circadian rhythm of breath hydrogen in young women.

Breath hydrogen levels, which reflect colonic fermentation of undigested starches, are usually low in the fasted state. Fasting levels of breath hydrogen are important for estimation of oro-cecal transit time and diagnosis of lactase deficiency. In young women, however, fasting levels of breath hydrogen are high. To clarify the reason for this, we studied the circadian pattern of breath hydrogen and the effect of alpha-D-galactosidase on fasting breath hydrogen in one study, and the effect of sleep deprivation on fasting breath hydrogen in another study, in 13 women students aged 21-23 years. In the first study, two breath samples were collected, one in the evening and the other the next morning. On another occasion, alpha-D-galactosidase was given before dinner and breath samples were collected the next morning. In the second study, the circadian rhythm of breath hydrogen was assessed for 3 days and the subjects were deprived of sleep on the second night. Breath samples were collected every 30 min, except during the second night when samples were collected at 1-h intervals. Fasting breath hydrogen was 24 +/- 3.9 ppm (mean +/- SE), which did not differ from the value for the previous night. Alpha-D-galactosidase significantly decreased fasting breath hydrogen levels, to 17 +/- 2.4 ppm (P < 0.05). There was a clear circadian pattern of breath hydrogen, high in the morning and decreasing to the nadir by 16:00. After dinner, the level increased again and stayed high during the night. Sleep deprivation did not affect fasting levels of breath hydrogen. High fasting breath hydrogen levels in young women followed a circadian pattern and this may have been due, in part, to an high intake of dietary fiber on the previous day.

Haemodynamics in children during rest and exercise: methods and normal values

Measuring haemodynamic performance in children is either invasive, and thus unacceptable, or noninvasive when the measured variable is often remote from the true variable. Measuring only maximum performance variables relies too heavily on motivation, especially in disease groups. We describe a method for the measurement of haemodynamic performance using respiratory mass spectrometry during rest, exercise and recovery therefrom. One hundred and six healthy children (55 male, 51 female) aged 8-16.9 yrs underwent an identical exercise protocol. Following studies at rest, they initially bicycled at 25 W x m(-2), increasing every 3 min by 15 W x m(-2) until exhaustion, after which measurements were made during recovery. Effective pulmonary blood flow, stroke volume, oxygen consumption, arteriovenous oxygen difference and functional residual capacity (FRC) together with estimates of pulmonary capillary blood volume and transit time were assessed at every exercise stage using inert gas rebreathing techniques. Haemodynamic performance is highly dependent on surface area, age, gender and pubertal stage. Many parameters, for example transfer factor, demonstrate pubertal stage-dependent differences at identical workloads even after correction for size. Females have a lower capillary blood volume at rest compared to age and size-matched males, but it is equalized during exercise. FRC unexpectedly rose with exercise, and peak exercise was associated with a falling stroke volume in 91% (95% CI 84-96%) of children, a possible demonstration of Starling's law of the heart. Oxygen pulse (oxygen consumption/cardiac frequency) is a very poor marker for pulmonary blood flow. Normal values are provided for all haemodynamic parameters for rest and every exercise stage for all subgroups of children. This should allow accurate comparison of normal and disease groups in future.

Simulating Migration Mortality of Atlantic Salmon Smolts in the Merrimack River

Abstract Successful restoration of Atlantic salmon Salmo salar to New England rivers involves the identification and management of mortality sources at different life history stages. The purpose of this study was to examine the effects of mortality during migration on Atlantic salmon smolts exiting the Merrimack River. Our objective was to review data pertaining to smolt production, migration, passage at hydroelectric facilities, and predation in the Merrimack River and construct a simulation model of smolt migration. We constructed a migration model incorporating river-flow-based decision rules affecting migration rate, delay at dams, dam passage mortality, and migration mortality. Mean model estimates of in-river survival ranged from 0.7% to 23.5%. Estimated transit times generally increased in migration scenarios in which smolts began migration later in the season; beginning migration later in the season also resulted in lower in-river survival. The model was evaluated by comparing records of returns o...

脈波伝搬時間の簡便計測法

In this study an experiment was carried out to establish a convenient method of Pulse Transit Time(PTT) estimation. The time interval between ECG R-wave and PTG(τ EP) were measured under cooling stimulation and the induced autonomic response was analyzed. ECG R-Wave was used as a reference timing for PTT measurement. It was possible to use the time from EGG R-wave to PTG(τ EP) as an ergonomic measure.

Dose–response effects of raw potato starch on small-intestinal escape, large-bowel fermentation and gut transit time in the rat

This study was designed to quantify starch digestion within the small and large bowels separately when raw potato starch (RPS) was included at 0-240 g/kg in diets fed to growing male Wistar rats. RPS was incorporated in the diets at the expense of maize starch which was expected to be almost completely digested in the small bowel. The digestibility of the maize starch was 0.99 but only 0.28 of the RPS was digested before the terminal ileum so that with increasing intakes of RPS there was a progressive increase in starch supply to the large bowel (LB). Of this starch 0.77, 0.72 and 0.73 was fermented in the large bowel when RPS constituted 80, 160 and 240 g/kg diet respectively. With increasing RPS intake, there was a curvilinear response in molar proportion of butyrate in caecal contents with a maximum value at about 80 g RPS/kg diet. The molar proportion of acetate increased linearly, that of propionate was unchanged, whilst proportions of the minor short-chain fatty acids all declined markedly with increasing RPS intake. The novel marker Bacillus stearothermophilus spores (BSS) was compared with CrEDTA in estimation of whole-gut mean transit time (MTT) when given together in a single test meal. Whilst estimates of MTT for the two markers were strongly correlated within individual rats (r2 0.72), BSS produced estimates that were 13 h longer than those based on CrEDTA. Neither marker detected a change in MTT with increasing RPS intake but, with both, the rate constant (k1) for the 'largest mixing pool' declined significantly (P < 0.001) as dietary RPS concentration was changed from 0-240 g/kg.

Regional perfusion parameters from pulmonary microfocal angiograms.

An indicator-dilution model was developed to describe transport of vascular contrast medium through an organ during acquisition of vascular dynamic contrast images. The model provides the theoretical basis for methods of determining regional blood flow, blood volume, and mean transit time from time-absorbance curves acquired from the images of tissue regions of interest (ROI) distal from the inlet site. The robustness of these methods was evaluated using a computer-simulated vessel network, which simulated the passage of a bolus of contrast medium through arterioles, networks of capillaries, and venules. The network was used to evaluate the reliability of ROI parameter estimation methods when the underlying model assumptions are violated. The shape of the ROI inlet concentration curve and moderate amounts of random noise did not affect the ability of the method to recover accurate parameter estimates. The estimates of ROI flow and transit time were degraded in the presence of significant dispersion of the inlet concentration curve as it traveled through arteries upstream from the microvascular ROI or when the flow was redistributed within the ROI. The estimates of ROI volume were relatively robust. The method was applied to image data of the dog pulmonary vasculature obtained using microfocal X-ray angiography to show that the results obtained from the simulations are consistent with actual data.

Reduced transit-time sensitivity in noninvasive magnetic resonance imaging of human cerebral blood flow.

Herein, we present a theoretical framework and experimental methods to more accurately account for transit effects in quantitative human perfusion imaging using endogenous magnetic resonance imaging (MRI) contrast. The theoretical transit time sensitivities of both continuous and pulsed inversion spin tagging experiments are demonstrated. We propose introducing a delay following continuous labeling, and demonstrate theoretically that introduction of a delay dramatically reduces the transit time sensitivity of perfusion imaging. The effects of magnetization transfer saturation on this modified continuous labeling experiment are also derived, and the assumption that the perfusion signal resides entirely within tissue rather than the arterial microvasculature is examined. We present results demonstrating the implementation of the continuous tagging experiment with delay on an echoplanar scanner for measuring cerebral blood flow (CBF) in normal volunteers. By varying the delay, we estimate transit times in the arterial system, values that are necessary for assessing the accuracy of our quantification. The effect of uncertainties in the transit time from the tagging plane to the arterial microvasculature and the transit time to the tissue itself on the accuracy of perfusion quantification is discussed and found to be small in gray matter but still potentially significant in white matter. A novel method for measuring T1, which is fast, insensitive to contamination by cerebrospinal fluid, and compatible with the application of magnetization transfer saturation, is also presented. The methods are combined to produce quantitative maps of resting and hypercarbic CBF.

Estimate of epididymal transit time in the chimpanzee

During their passage through the epididymis, sperm undergo functional changes which result in their maturation and in their ability to fertilize ova. Maturational changes effected during epididymal transport are attributable to sequential changes in various regions of the plasmalemma of the sperm head and flagella. These functional changes in the plasmalemma result, at least in part, from the sequential binding of proteins secreted by the epididymal epithelium into the epididymal lumen. An estimate of epididymal transit time is essential to such investigations. Time elapsed from a testicular arterial infusion of a single pulse of tritiated-thymidine to the release of 3H-labeled sperm into the lumen of the seminiferous tubule was about 39 days. Seminal fluid-free 3H-labeled sperm first appear in the ejaculate about 41±1 days post-infusion. Total transit time for 3H-labeled Sd2 sperm released into the tubular lumen to appear in the ejaculate is estimated as the difference between these values. Since total transit time is equal to the seminiferous tubule transit time plus the epididymal transit time, epididymal transit time constitutes some lesser portion of the total transit time of 2±1 days.

Radiological bile acid absorption test 75SeHCAT in patients with diarrhoea of unknown cause.

The purpose with this study was to investigate the usefulness of the 75SeHCAT test in patients suffering from "functional" diarrhoea and to disclose earlier radiological investigations performed in the course of disease. Twenty patients with chronic diarrhoea of unknown cause were investigated with the 75SeHCAT test. The cholestyramine test and an estimation of oro-caecal transit time (OCTT) were also performed in 13 and 10 patients respectively. Ten patients had low 7-day retention (< or = 15%). Nine of these were tested with cholestyramine and 8 showed complete relief from the diarrhoea. The cholestyramine test had no effect on the 4 patients with normal bile acid retention. No correlation was found between the retention of 75SeHCAT and OCCT. A total of 80 inconclusive gastrointestinal barium examinations were performed during the course of disease. Pathological bile acid retention, studied with the radiological 75SeHCAT test, is common in patients with diarrhoea of unknown cause. The test should be performed earlier in the course of disease in order to prevent unnecessary radiological investigations and to reduce patient suffering and distress.

Pulmonary distribution of alfentanil and sufentanil studied with system dynamics analysis.

We applied a system dynamics approach to the study of the pulmonary distribution of alfentanil and sufentanil in anesthetized pigs and patients, respectively. This method allows estimation of the mean transit time through the lungs and calculation of the volume of distribution of alfentanil in the lungs. In the first part of the study the pulmonary distribution of alfentanil was studied in six anesthetized pigs during three hemodynamic states (control, partial clamping of the inferior vena cave, and complete clamping of the right pulmonary artery). In the second part of the study the pulmonary distribution of sufentanil was studied in 10 patients, scheduled for elective CABG, during and after a constant rate infusion of 10 min. Pulmonary passage of the opioids was characterized by functions of transit times, derived from the pulmonary arterial and systemic arterial concentration curves. Pulmonary distribution volumes were calculated from the mean transit time and pulmonary blood flow. Pulmonary distribution volume of alfentanil during the control measurement was significantly higher (486 +/- 88 ml) than during either partial caval clamping (346 +/- 89 ml, p < 0.05) or right pulmonary artery clamping (336 +/- 56 ml, p < 0.05). There was no change in the extravascular volume of distribution of alfentanil with each hemodynamic state. Pulmonary volume of distribution of sufentanil in the patients was 22.6 (10.9) L. Pulmonary distribution of opioids can be studied using system dynamics analysis, both after bolus injection and during and after infusion. This method can be used for periods beyond the initial passage of the drug through the lungs.